Instrument level switch type TX/S/HC/0750/11/2/HO/FMX by K-Tek how does it work when reaching the water?

Question

This instrument is a detecting water and sand. how can it destinguesh the water and sand? how can you calibrate for this two component?

Answer 1

This instrument is measuring the change in thermal conductivity of its surrounding material. It does this by monitoring the temperature of a small heater(heat Xmit) and comparing that temperature to a nearby temp sensor(heat Rcvr).

If the sensor is in air which is a poor thermal conductor then not much heat will be conducted over to the Heat Rcvr element from the Heat Xmit element.

Have a liquid like water which conducts heat cover the elements then the temperature will rise in the heat rcvr. This change in temperature is what triggers the switch. (most likely done by a comparator circuit as the set point is ajusted by a variable resistor.

This sensor can also distinguish a change in flow rate. Still or very slow moving water will allow the Heat Recvr temperature to rise. Increase the flow and you will increase the convective losses and cause the Heat Rcvr to cool. Again changes in temperature of the rcvr will trigger the switch.

This type of sensor can distinguish between different types of materials if there is a significant difference in thermal conductivity between the material types. (Air and water) or (Air and Oil) or (Water and Oil) provided that there is not a significant change in flow across the sense elements. ( A flow change could be interpreted as an interface detection)

To detect sand in water there would have to be a difference in thermal conductivity between water and sand. Sand would be a heat insulator and water a heat conductor. Also a slight water flow across the sense element could be detected as well . Covering the element with sand would also block and/or significantly alter the heat transfer of the flowing water.

To calibrate for two components the unit would have to have a dual output capability and dual setpoints. You would be combining two units into one. (Is this available) Each set point would be set for the different temperatures generated by the multiple materials. You may find that as temperature changes occurr due to a level or flow change by material A. The thermal excursion sensed by the Heat Rcvr may first enter the detection region for Material B. (So did the empty tank first get filled with water then Sand?) OR (Did Sand just fill the tank without any water)

You will probably have to use seperate sensors in different locations in areas that are only likely to see two types of materials.

Air Liquid interface at a high(er) location and a Sand Liquid interface at a low location